The present application is related to the subject matter of U.S. application Ser. No. 08/131,473, filed Oct. 4, 1993, which is a continuation-in-part application of U.S. application Ser. No. 07/885,194, filed May 19, 1992, now abandoned, entitled "Phased Chain Assemblies" which is incorporated herein by reference.
The present invention relates generally to power transmission chains. The invention has particular application to power transmission chains of the inverted tooth or silent chain variety, which are used in engine timing applications as well as in the transfer of power from a torque converter to a transmission or in a transfer case of a four-wheel-drive vehicle. The invention includes a chain assembly of inverted tooth links having a single sprocket engaging toe to transfer power between the chain assembly and an associated sprocket.
Power transmission chains are widely used in the automotive industry. Such chains are used for engine timing drives as well as for the transfer of power from a torque converter to the transmission or for the transfer of power in a transfer case. Power transmission chains are also widely used in industrial applications.
One type of power transmission chain is referred to as "silent chain". Such chain is formed of interleaved sets of inverted tooth links. A set or rank of links is assembled from several links positioned alongside of or adjacent to each other. The links are connected by pivot means, which are typically round pins received in a pair of apertures. An example of silent chain is found in U.S. Pat. No. 4,342,560, which is incorporated herein by reference. Another example of silent chain is found in U.S. Pat. No. 4,915,675, which is also incorporated herein by reference.
Conventional silent chains typically include both guide links and articulating links. The guide links are positioned on the outside edges of alternate sets of links. The guide links act to position the chain laterally on the sprocket. Guide links typically do not mesh with the sprocket teeth.
The inverted tooth links, or sprocket engaging links, provide the transfer of power between the chain and sprocket. Each inverted tooth link typically includes a pair of apertures and a pair of depending toes or teeth. Each toe is defined by an inside flank and an outside flank. The inside flanks are joined at a crotch. The inverted tooth links are typically designed so that the links contact the sprocket teeth to transfer power between the chain assembly and the sprocket. The inverted tooth or driving links contact the sprocket teeth along their inside link flanks or their outside link flanks or combinations of both flanks. The contacts between the flanks and the sprocket teeth can be of the type which provide a power transfer, or can be of the nature of an incidental or secondary contact.
A conventional silent chain drive is comprised of an endless silent chain wrapped about at least two sprockets supported by shafts. Movement of a driving sprocket causes power transmission through the chain and consequent movement of a driven sprocket. In an engine timing drive application, the driving sprocket is mounted on the engine crankshaft and the driven sprocket(s) mounted on one or more camshafts. The rotation of the camshaft(s) is thus controlled by the rotation of the crankshaft through the chain.
Noise is associated with such chain drives. Noise is generated by a variety of sources, but in silent chain drives it can be caused, in part, by the impact sound generated by the collision of the chain and the sprocket at the onset of meshing. The loudness of the impact sound is affected by, among other things, the impact velocity between the chain and the sprocket.
The meshing impact sound is generally a periodic sound in chain drives. The impact sound is repeated with a frequency generally equal to that of the frequency of the chain meshing with the sprocket. The frequency is related to the number of teeth on the sprocket and the speed of the sprocket. The impact can produce sound having objectionable pure sonic tones.
Another cause of noise in chain drives is the chordal action of the sprockets as the chain is driven about the sprockets. The meshing of the chain and sprocket at the chain mesh frequency can cause a movement of the free chain strand or span (the part of the chain between the sprockets) in a direction perpendicular to the chain travel but in the same plane as the chain and sprockets. This vibratory movement can also produce an objectionable pure sonic tone at the frequency of the chain mesh frequency or a derivative of it.
Many efforts have been made to decrease the noise level in chain drives of the silent chain variety by minimizing the objectionable effects of the pure sonic tones. The problem of noise reduction in silent chain drives was addressed in U.S. Pat. No. 4,342,560 by changing the contacts between the link flanks of a silent chain and the sprocket teeth by having differently configured link flanks in different sets of the chain. By mixing links of differing flank configuration, U.S. Pat. No. 4,342,560 attempted to modify the pattern of sound emanating from the chain contacting the sprocket by altering the types of link configurations and thus altering the point and rhythm of contacts. U.S. Pat. No. 4,915,675, which is incorporated herein by reference, utilized the same concept of modifying the pattern of sound emanating from the chain by altering the types of link configurations. That patent teaches the utilization of an asymmetrically shaped link form which is then oriented in two different directions in the chain assembly to alter the point and rhythm of chain to sprocket contacts.
Other attempts to alter the rhythm of contacts between the silent chain drive and the sprocket have focused on the modification of the sprocket teeth. For example, U.S. Pat. No. 3,377,875 and U.S. Pat. No. 3,495,468, teach relief of some of the sprocket teeth, or even elimination of some teeth, in order to achieve noise reduction in contacts between the links of the silent chain and the sprocket teeth.
The present invention utilizes an asymmetrical link to alter the point and rhythm of chain to sprocket contacts. The present invention seeks to provide a silent chain construction that modifies the pattern of chain and sprocket contacts and achieve noise reduction through the use of single toe links in the chain assembly.
Prior art chains have utilized single toe links. For example, U.S. Pat. No. 959,046 discloses a single toe guide link. However, the guide links act only to maintain the chain assembly on the sprockets. The guide links do not provide direct power transfer to or from the sprocket and thus do not impact the sprocket at the chain mesh frequency. Hence, the use of single toe guide links does not effect the noise spectrum produced by the articulating links.
U.S. Pat. No. 579,742 discloses a chain with single toe links that are located slightly off-center. The links engage the sprocket through antifriction balls that are trapped in sprocket cavities. All of the links of the chain have single toes.
U.S. Pat. No. 637,056 shows a chain with single toe links that are substantially centrally located. The patent discloses a chain having cylindrical sprocket teeth that come into contact with the link toe at its base. The contact of the link and the cylindrical toe is intended to occur on both sides of the toe. All of the links of the chain are single toe.
The single toe links in the present invention are utilized as the sprocket engaging links, or non-guide links, in an attempt to modify the pattern of contacts between the chain and the sprocket. In addition, because single toe links are of lighter weight construction, this may provide a significant advantage in certain mass sensitive applications.